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Register a new userFrom Colors to Chemistry: A Combined Lenslet/Slicer IFS for Medium-Resolution Spectroscopy
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We present the design and lab performance of a prototype lenslet-slicer hybrid integral field spectrograph (IFS), validating the concept for use in future instruments like SCALES/PSI-Red. By imaging extrasolar planets with IFS, it is possible to measure their chemical compositions, temperatures and masses. Many exoplanet-focused instruments use a lenslet IFS to make datacubes with spatial and spectral information used to extract spectral information of imaged exoplanets. Lenslet IFS architecture results in very short spectra and thus low spectral resolution. Slicer IFSs can obtain higher spectral resolution but at the cost of increased optical aberrations that propagate through the down-stream spectrograph and degrade the spatial information we can extract. We have designed a lenslet/slicer hybrid that combines the minimal aberrations of the lenslet IFS with the high spectral resolution of the slicer IFS. The slicer output f/# matches the lenslet f/# requiring only additional gratings.
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Integral Field Spectroscopy (IFS) is a technique that gives simultaneously the spectrum of each spatial sampling element in a given object field. It is a powerful tool which rearranges the data cube (x, y, lambda) represented by two spatial dimensions defining the field and the spectral decomposition in a detector plane. In IFS, the spatial unit reorganizes the field and the spectral unit is being composed of a classical spectrograph.The development of a Collimating Slicer aims at proposing a new type of integral field spectrograph which should be more compact. The main idea is to combine the image slicer with the collimator of the spectrograph, thus mixing the spatial and spectral units. The traditional combination of slicer, pupil and slit elements and the spectrograph collimator is replaced by a new one composed of a slicer and collimator only. In this paper, the state of the art of integral field spectroscopy using image slicers is described. The new system based onto the development of a Collimating Slicer for optical integral field spectroscopy is depicted. First system analysis results and future improvements are discussed. It finally turns out that this new system looks very promising for low resolution spectroscopy.
In this article we present the integral field spectroscopy (IFS) wiki site, http://ifs.wikidot.com; what the wiki is, our motivation for creating it, and a short introduction to IFS. The IFS wiki is designed to be a central repository of information, tips, codes, tools, references, etc., regarding the whole subject of IFS, which is accessible and editable by the whole community. Currently the wiki contains a broad base of information covering topics from current and future integral field spectrographs, to observing, to data reduction and analysis techniques. We encourage everyone who wants to know more about IFS to look at this web-site, and any question you may have you can post from there. And if you have had any experience with IFS yourself, we encourage you to contribute your knowledge and help the site develop its full potential. Before re-inventing the wheel, consult the wiki...
CYCLOPS2 is an upgrade for the UCLES high resolution spectrograph on the Anglo-Australian Telescope, scheduled for commissioning in semester 2012A. By replacing the 5 mirror Coude train with a Cassegrain mounted fibre-based image slicer CYCLOPS2 simultaneously provides improved throughput, reduced aperture losses and increased spectral resolution. Sixteen optical fibres collect light from a 5.0 arcsecond^2 area of sky and reformat it into the equivalent of a 0.6 arcsecond wide slit, delivering a spectral resolution of R = 70000 and up to twice as much flux as the standard 1 arcsecond slit of the Coude train. CYCLOPS2 also adds support for simultaneous ThAr wavelength calibration via a dedicated fibre. CYCLOPS2 consists of three main components, the fore-optics unit, fibre bundle and slit unit. The fore optics unit incorporates magnification optics and a lenslet array and is designed to mount to the CURE Cassegrain instrument interface, which provides acquisition, guiding and calibration facilities. The fibre bundle transports the light from the Cassegrain focus to the UCLES spectrograph at Coude and also includes a fibre mode scrambler. The slit unit consists of the fibre slit and relay optics to project an image of the slit onto the entrance aperture of the UCLES spectrograph. CYCLOPS2 builds on experience with the first generation CYCLOPS fibre system, which we also describe in this paper. We present the science case for an image slicing fibre feed for echelle spectroscopy and describe the design of CYCLOPS and CYCLOPS2.
Large imaging arrays of detectors at millimeter and submillimeter wavelengths have applications that include measurements of the faint polarization signal in the Cosmic Microwave Background (CMB), and submillimeter astrophysics. We are developing planar lenslet arrays for millimeter-wavelength imaging using metamaterials microlithically fabricated using silicon wafers. This metamaterial technology has many potential advantages compared to conventional hemispherical lenslet arrays, including high precision and homogeneity, planar integrated anti-reflection layers, and a coefficient of thermal expansion matched to the silicon detector wafer. Here we describe the design process for a gradient-index (GRIN) metamaterial lenslet using metal-mesh patterned on silicon and a combination of metal-mesh and etched-hole metamaterial anti-reflection layers. We optimize the design using a bulk-material model to rapidly simulate and iterate on the lenslet design. We fabricated prototype GRIN metamaterial lenslet array and mounted it on a Polarbear/Simons Array 90/150~GHz band transition edge sensor (TES) bolometer detector array with sinuous planar antennas. Beam measurements of a prototype lenslet array agree reasonably well with the model simulations. We plan to further optimize the design and combine it with a broadband anti-reflection coating to achieve operation over 70--350~GHz bandwidth.
We present an automated statistical method that uses medium-resolution spectroscopic observations of a set of stars to select those that show evidence of possessing significant amounts of neutron-capture elements. Our tool was tested against a sample of $sim 70,000$ F- and G-type stars distributed among $215$ plates from the Galactic Understanding and Exploration (SEGUE) survey, including $13$ that were directed at stellar Galaxy clusters. Focusing on five spectral lines of europium in the visible window, our procedure ranked the stars by their likelihood of having enhanced content of this atomic species and identifies the objects that exhibit signs of being rich in neutron-capture elements as those scoring in the upper $2.5%$. We find that several of the cluster plates contain relatively large numbers of stars with significant absorption around at least three of the five selected lines. The most prominent is the globular cluster M3, where we measured a fraction of stars that are potentially rich in heavy nuclides, representing at least $15%$.
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